Characterization of Particles During Growth in Emulsifier-Free Emulsion Polymerization of Styrene

Summary

The emulsion polymerization of styrene in water in the absence of added surfactant has been studied by analyzing samples removed from the reaction vessels at various times. The particles present within these samples were characterized by electron microscopy, gravimetric analysis, gel permeation chromatography, conductometric titration and gas adsorption. During the early stages of reac tion, the number of particles decreased very rapidly to a level which then remained constant throughout the rest of the reaction. The particles in the early stages when N was decreasing appeared to consist mainly of polymer of about 1000 M.Wt., a small amount of high M.Wt. polymer was also present. The presence of this low molecular weight polymer may indicate that particle nucleation occurs either by the precipitation or micellization of low (500) M.Wt. oligomers. When N became constant, the growth of the particles was well described by a square law relationship between radius and time. The presence of particles of non-uniform electron density was noted and investigated. The particle nucleation was also studied using a combination of total intensity light scattering and photon correlation spectroscopy in a study of unstirred systems. The results indicated that in such unstirred systems, the particles were present as aggregates. The surface charge of the particles was found to decrease slowly between 20 – 30% conversion and then to remain almost constant throughout the rest of the reaction.